1. Field of the Invention
This invention relates to an aqueous iminocarboxylic acid salt solution composition and a method for the handling of an iminocarboxylic acid salt. More particularly, it relates to the aqueous solution composition of an iminocarboxylic acid salt useful as an organic chelating agent, a detergent builder, a descaling agent, etc. and a method for handling the iminocarboxylic acid salt in the form of a stable and homogeneous aqueous solution without entraining precipitation of iminocarboxylic acid salt crystals for a long time.
The term "handling" as used in this invention refers to the transportation of the aqueous solution of an iminocarboxylic acid salt as by means of a tank lorry, the storage thereof as in a tank, the conveyance thereof as by a piping inclusive of pipes, valves, and nozzles, and the like.
2. Description of the Prior Art
The iminocarboxylic acid salts which are represented by such formula (I) and formula (II) as will be described specifically afterward have been known because of their disclosure in JP-A-05-170,714. When such an iminocarboxylic acid salt as mentioned above is handled in a solid state such as of a powder or granules, since this salt has high hygroscopicity, the individual solid particles thereof in the course of handling absorb the moisture suspended in the ambient air and ultimately form viscous lumps by virtue of fusion.
It is, accordingly, proper to handle the iminocarboxylic acid salt in the form of an aqueous solution. No concrete study has ever been made as to the handling of the salt in the form of an aqueous solution. For the first time in the art, our study has confirmed that various problems are encountered in the handling of the iminocarboxylic acid salt in the form of an aqueous solution. One of the problems resides in the precipitation of the salt in the aqueous solution. Generally, it is economical to handle this aqueous solution at its highest allowable concentration at a low temperature. Under the conditions of such high concentration and such low temperature, however, the aqueous solution precipitates iminocarboxylic acid salt crystals and particularly the elapse of time proportionately aggravates this precipitation. In an extreme case, the precipitation may end up in solidification of the whole of the aqueous solution itself. Especially, for the sodium salt of an iminocarboxylic acid, the problem of this precipitation is serious because this salt is deficient in solubility in water as compared with other salts of the acid. Another problem consists in the viscosity of the aqueous iminocarboxylic acid salt solution. If the aqueous solution avoids precipitating such crystals and nevertheless exhibits such high viscosity as exceeds 10,000 cps, the difficulty with which it is handled will be exaggerated notably. Yet another problem resides in the fact that an attempt to heighten the concentration of the aqueous solution of an iminocarboxylic acid salt to a desired level by heating this solution results in coloring the iminocarboxylic acid salt or the aqueous solution thereof possibly to the extent of seriously impairing the commercial value thereof and moreover inducing the precipitation of the iminocarboxylic acid salt in the aqueous solution.
An object of this invention, therefore, is to provide a novel aqueous solution composition of an iminocarboxylic acid salt and a method for handling the composition.
Another object of this invention is to provide the aqueous solution composition of an iminocarboxylic acid salt so stable that the composition, when used as a chelating agent, for example, permits easy handling in the form of a homogeneous solution and avoids precipitating crystals even at low temperatures.
Yet another object of this invention is to solve the afore-mentioned problems which are encountered when an iminocarboxylic acid salt is handled in the form of an aqueous solution and provide a method for enabling the aqueous iminocarboxylic acid salt solution to be stably handled for a long time.